The present invention relates to a process and apparatus for manufacturing pneumatic tires and, more particularly, to those steps for manufacturing a pneumatic tire carried out subsequent to the formation of a carcass in a cylindrical configuration.
As is known, a carcass can be made on a single drum arranging the various reinforcing plies in the form of a cylindrical sleeve, then applying the bead cores on the ends of the plies, consequently expanding the suitable seats provided on the drum to oblige the plies to abut around the bead cores and at last expanding the central portion of the drum and drawing simultaneously the bead core seats toward one another to shape the carcass in a toric form. In a further step there is effected the turn-up of the ends of the plies on the sidewalls of the carcass and the application of the reinforcing annular structure and of the tread.
The method can cause, in some cases, an unacceptable skidding of the plies around the bead cores during the step of torically shaping the carcass as a result of the strong tensile stresses on the cords of the plies themselves determined by high inflation pressures. The main skidding cause is bound to a certain bending stiffness of the carcass plies so that the plies themselves do not perfectly abut around the bead cores when the seats of the drum are expanded to determine the anchoring between the plies and the bead cores.
A possible solution to remedy the cited drawback could be that of building up separately the carcass using suitable means designed to faithfully conform the plies around the sides of the bead cores so as to realize a carcass tube to be then transported to an expandable drum to develop the tube from the cylindrical to the toric configuration. However, even if at first glance this procedure appears to be an immediate solution, practically it is considered to give rise to other various problems to be solved all at the same time. First, there is to bear in mind the present inadequacy of the known expandable drums to receive a carcass tube having two sections of reduced diameter at a distance from the ends and in correspondence to the zone of the bead cores. In fact, no solution exists in respect to an automatic loading of a tube having variations in diameter comprising reductions in sections. On the other hand, it is impossible to think of effecting a manual loading of such a tube around a drum of known type, since even admitting to be able to carry out this loading, the carcass would tend to be deformed in the anchoring zones of the plies to the bead cores altering the above-cited faithful coupling and annulling the advantages of making a tube separately. Thus, it is necessary to dispose of appropriate seats on the drum in order to clamp, with the necessary pressure the already preconstituted annular blocks formed by the bead cores with the plies wound on the sides thereof.
Therefore, it is an object of the present invention to provide a process for manufacturing pneumatic tires which will overcome the above-noted and other disadvantages.
A further object of the present invention is to provide a novel method for manufacturing pneumatic tires comprising a carcass formed by one or more reinforcing plies, a pair of bead cores, a tread and a reinforcing annular structure between the carcass and tread.
Still, a further object of the present invention is to provide a method using novel apparatus for manufacturing pneumatic tires comprising a carcass formed by one or more reinforcing plies, a pair of bead cores, a tread and a reinforcing annular structure.